Although it entered service in 1947, the Thunderjet was plagued by such a large amount of structural and engine problems that a 1948 U.S. Air Force review declared it unable to execute any aspect of its intended mission and considered canceling the program.

Over half of the 7,524 F-84s produced served with NATO nations, and it was the first aircraft to fly with the U.S. Air Force Thunderbirds demonstration team.

Modified F-84s were used in several unusual projects, including the FICON and Tom-Tom dockings to the B-29 Superfortress and B-36 bomber motherships, and the experimental XF-84H Thunderscreech turboprop.

The F-84F swept wing version was intended to be a small variation of the normal Thunderjet with only a few different parts, so it kept the basic F-84 number.

In 1944, Republic Aviation's chief designer, Alexander Kartveli, began working on a turbojet-powered replacement for the P-47 Thunderbolt piston-engined fighter aircraft.

The initial attempts to redesign the P-47 to accommodate a jet engine proved futile due to the large cross-section of the Thunderbolt's fuselage.

[3][2] Since the design promised superior performance to the Lockheed-built P-80 Shooting Star and Republic had extensive experience in building single-seat fighters, no competition was held for the contract.

[6][7] Meanwhile, wind tunnel testing by the National Advisory Committee for Aeronautics revealed longitudinal instability and stabilizer skin buckling at high speeds.

[6][7] The results of this preliminary testing were incorporated into the third prototype, designated XP-84A, which was also fitted with a more powerful J35-GE-15 engine with 4,000 lbf (17.79 kN) of thrust.

[12][13] The F-84B, which differed from the YP-84A only in having faster-firing M3 machine guns (later F-84s also had provision to carry eight 5 in (130 mm) High Velocity Aircraft Rockets (HVAR) underwing[14][10]), became operational with 14th Fighter Group at Dow Field, Bangor, Maine, in December 1947.

It had been discovered that the untested wingtip fuel tanks contributed to wing structural failures by inducing excessive twisting during high-g maneuvers.

The actual flight hours for Korean War and NATO deployments rapidly outpaced the supply and Allison's ability to manufacture new engines.

[26] The final straight-wing F-84 was the F-84G, intended as a stop-gap until the swept wing F-84F entered service, but ordered in large numbers to build-up NATO air forces.

[22] It introduced a refueling boom receptacle in the left wing,[27][28][29] autopilot, Instrument Landing System, J35-A-29 engine with 5,560 lbf (24.73 kN) of thrust, a distinctive framed canopy (also retrofitted to earlier types), and the ability to carry a single Mark 7 nuclear bomb.

In hot Korean summers with a full combat load, the aircraft routinely required 10,000 ft (3,000 m) of runway for takeoff even with the help of RATO bottles (two or four of these were carried, each producing 1,000 lbf (4.4 kN) of thrust for 14 seconds).

[34] Thanks to the thick straight wing the Thunderjet rapidly reached its Mach 0.82 limitation at full throttle and low altitude.

The aircraft had sufficient power to fly faster, but exceeding the Mach limit at low altitudes resulted in a violent pitch-up and structural failure causing the wings to break off.

Slower than the MiG, the F-84 was also unable to turn tightly with a maximum instantaneous-turn load of only 3 gs followed by rapid loss of airspeed.

[38] It was also called "The Iron Crowbar", "a hole sucking air", "The Hog" ("The Groundhog"), and "The World's Fastest Tricycle", "Ground Loving Whore" as a testament to its long takeoff rolls.

[39] F-84 lore stated that all aircraft were equipped with a "sniffer" device that, upon passing takeoff safety speed, would look for the dirt at the end of the runway.

[40] While the F-84B and F-84C could not be deployed overseas because their J35 engines had a service life of only 40 hours, the F-84D and F-84E were more suitable,[41] and so the F-84E-equipped 27th Fighter Escort Group was sent to the Far East aboard the aircraft carrier Bataan, which arrived in Japan on 30 November 1950.

[43] The number of units operating the F-84 over Korea gradually increased, both by bringing over Air National Guard Groups from the US, and converting F-80 squadrons already in theater.

[48][49] Portugal received its first F-84s in January 1953, with 25 new build F-84Gs later supplemented by USAFE stocks and from other European operators, with deliveries eventually reaching 125 F-84Gs.

[51] Two squadrons were formed in Portugal, operating the F-84 in both air-defense and ground attack roles,[52] with the Thunderjet also equipping an aerobatic display team, the Dragões.

[55][56] In 1966, after Rhodesia's Unilateral Declaration of Independence, and the imposition of the Beira Patrol by the British Royal Navy to attempt to stop the flow of fuel to Rhodesia via the port of Beira, Mozambique, a detachment of eight F-84s was sent from Luanda to Mozambique to guard against potential clashes with British forces, with the aircraft returning to Angola when the threat of military action receded.